Diffusion

1. a) Bulk movement is the overall movement of a fluid. The molecules all
move in the same direction. Diffusion however is the random movement of
molecules which usually results in a fairly even distribution. In other
words the movement is not guaranteed to move in one direction but the
probability that it will move in the lower gradient is greater. Osmosis is
similar to diffusion but is differentiated by the membrane\'s behavior. The
cell membrane does allow water to move from higher to lower concentrations
but does not allow solutes do that. b) Water potential is the capacity of
water to move to a from a region where there is high water potential to low
water potential. This action happens without the affect of outside forces.
When outside actions due occur and they give water a high potential energy
than the water will move to the region where less potential energy is.
Hydrostatic pressure is the pressure required to stop water the movement of
water. This is a method of measurement. The osmotic potential is the
measure of tendency of water to move through a membrane which contains a
solution. This occurs when a cell does not allow a hypertonic solution to
leave the cell membrane. The cell begins to increase with water but the
cell membrane can not release the solution and thus the water potential
within the cell increases. This causes the water to no longer enter the
cell. c) Hypotonic is less solute to a certain amount of water. Hypertonic
is more solute to a certain amount of water. Isotonic is the equal amount
of solutes in two different solutions. d) Endocytosis is the inward bulge
causes by incoming molecules. Exocytosis is the expelling of a material
outside a cell. e) Phagocytosis is the process where the cell obtains
solid matter. This is different from the pinocytosis where the cell
obtains liquid matter. These both are endocytic processes.
Receptor-mediated endocytosis is the process where there are interactions
between a material and receptor sites on the cell. In this process the
cell accepts the material if it matches with the receptor sites. f) Coated
pits are areas which peripheral proteins indent the membrane. This is
where the vesicles for certain materials are formed. The vesicle which is
formed is called the coated vesicle. g) Plasmodesmata are the links
which hold two adjacent cells together. Gap junctions are the channels
which allow materials to flow between cells.
2. The concentration gradient is the difference in the density of a
material from one region to another region. The concentration gradient
affects diffusion by allowing the substance to flow from high concentration
to low concentration. The concentration gradient affects osmosis by the
same manner it does in diffusion. The cell does not allow the solution to
exit the cell when water is entering. This keeps the solution in the cell
making the concentration high and thus no further penetration of water.

4. Diffusion is more rapid in gases because they are less dense than
liquids. They repel each other more resulting in faster diffusion.
Diffusion is greater at higher temperatures because of the greater kinetic
energy among the molecules. They push each other more making them less
dense.

5. The concentration of the solute is 1%. This happens because a 1% sugar
solution is isotonic with that of the 1% sugar solution in the tubes. The
2% sugar solution was increased because the substance was hypertonic. The
membrane did not allow the hypertonic solution to exit because the pressure
from the hypotonic solution was forcing water in. This later reached an
equilibrium when the hypertonic solution was gaining water potential and
the water stopped rising. The vice versa happened in the distilled water
solution.